Brake actuating and adjusting mechanism

ABSTRACT

A brake mechanism having a pressure actuated piston moving disc brake pad assemblies into braking engagement with a disc for service brake operation, and a mechanically actuated mechanism which mechanically moves the piston to engage the brake pad assemblies with the disc for a parking brake operation. The piston has a screw and an adjuster nut threaded thereon, the nut being restrained from excess axial movement relative to a mechanically actuated shaft in one direction and a housing containing the piston and shaft in the other direction. The nut forms a part of a clutch arrangement which is actuated by the mechanically actuated shaft so that operative force transmitting engagement can occur between the shaft and the piston. The adjuster nut provides for clearance take-up and adjustment for lining wear during pressure brake actuation.

United States Patent [191 Brooks [4 1 Oct. 16, 1973 [54] BRAKE ACTUATINGAND ADJUSTING MECHANISM [75] Inventor: Frank W. Brooks, Dayton, Ohio[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Oct. 30, 1972 [21] Appl. No.: 302,082

[56] References Cited UNITED STATES PATENTS 8/1971 Marschall et al.188/196 D 4/1973 Evans 188/71.9X

Primary Examiner-Duane A. Reger Att0mey-W. S. Pettigrew et al.

[5 7 ABSTRACT A brake mechanism having a pressure actuated piston movingdisc brake pad assemblies into braking engagement with a disc forservice brake operation, and a mechanically actuated mechanism whichmechanically moves the piston to engage the brake pad assemblies withthe disc for a parking brake operation. The piston has a screw and anadjuster nut threaded thereon, the nut being restrained from excessaxial movement relative to a mechanically actuated shaft in onedirection and a housing containing the piston and shaft in the otherdirection. The nut forms a part of a clutch arrangement which isactuated by the mechanically actuated shaft so that operative forcetransmitting engagement can occur between the shaft and the piston. Theadjuster nut provides for clearance takeup and adjustment for liningwear during pressure brake actuation.

2 Claims, 1 Drawing Figure 1 BRAKE ACTUATING AND ADJUSTING MECHANISM Theinvention relates to a mechanism for actuating the brake shoes of apressure actuated disc brake so as to maintain brake adjustment and toalso actuate the brake by manual application to provide a parking brakemode of operation. The parking brake mechanism changes rotational orarcuate motion of an actuated lever to linear motion of the pressureactuated piston, and provides an arrangement for compensating for brakelining wear and for compensating for lining swell or growth. A high-leadscrew and nut arrangement with a clutch mechanism is utilized, axialmovement of the nut being limited by a restrainer device. The restrainerdevice, in combination with the clutch mechanism, establishes the normaland maximum brake lining clearances obtainable with the brakes properlyadjusted.

IN THE DRAWING The single FIGURE is a cross-section view, with partsbroken away, of a disc brake assembly embodying the invention.

The general assembly includes a fixed caliper frame and support unit 10,a disc 12, a wheel assembly 14 including a brake disc drive and supportmember 16 and a wheel 18, a wheel disc section 20 and a wheel rimsection 22. The wheel assembly also includes a hub, the hub flange 24being shown in the drawing, to which the wheel disc section 20 and thebrake disc drive and support member 16 are attached by means of bolts 26and nuts 28.

The disc 12 is illustrated as being of the annular type with the outerperiphery 30 being notched'to receive circumferentially spaced fingers32 of the member 16 so that the disc is axially slidable relative to themember 16. The disc 12 has opposed friction surfaces 34 and 36 whichextend within the U-shaped fixed caliper frame 38.

The caliper frame 38 is a part of the fixed caliper frame and supportunit and has two radially outwardly extending legs 40 and 42 which areaxially spaced and joined by a bridge section 44 extending through theanulus of the disc 12. The support flange 46 is secured to the caliperframe 38 and is also suitably fixed to a non-rotating portion of thevehicle such as an axle housing or a steering knuckle.

Leg 42 of the caliper frame includes a housing 48 which forms a cylinderbody 50. The portion of the leg 42 from which housing 48 is formed hasan opening therein facing the disc 12 and providing a cylinder wall 52which is at the entry to the pressure chamber 54, also provided inhousing 48. A base or end wall 56 of chamber 54 is formed from housing48 and closes the outer end of chamber 54. A pressure actuated piston 58is reciprocably received in chamber 54 and is sealed at cylinder wall 52by the piston seal 60. A suitable boot62 closes the outer end of chamber54 to protect the piston and cylinder walls against contamination.

The brake pad assemblies 64 and 66 are mounted on the caliper frame 38so that they transmit brake torque to the caliper frame. In addition tobeing mounted on the caliper frame 38, brake pad assembly 64 is mountedon leg 40 while brake pad assembly 66 is mounted on the head 68 ofpiston 58.

The pad assemblies respectively comprise shoes 70 and 72 to which brakelinings 74 and 76 are suitably attached so as to frictionally engagefriction disc surfaces 34 and 36 when the brakes are actuated. The outersides of the brake shoes and 72 are respectively provided with one ormore bosses 78 and 80. The bosses aid considerably in locating the brakepad assemblies. Boss 80 of brake pad assembly 66 extends into adepression 82 formed in the outer side of the piston head 68 so that thepiston cannot rotate for any substantial arcuate distance in thecylinder 52. Thus, the brake pad assembly provides means for normallypreventing rotational movement of the piston.

Piston 58 also has a piston skirt section 84 extending away from head 68and into chamber 54. The skirt provides a recess 86 which is a part ofpressure chamber 54. The skirt inner wall has a plurality of splines 88extending axially parallel to the piston. A high-lead threaded screw 90is secured to the piston head 68 by suitable means such as having oneend press fitted in a recess 92, the threaded portion of the screw 90extending along the axis of the piston 58 through recess 86 and intochamber 54.

The base wall 56 of cylinder body 50 receives an actuating shaft 94therethrough in reciprocal and rotatable relation, the shaft beingprovided with a seal 96 to seal pressure chamber 54. Shaft 94 has anouter end 98 to which an actuating lever 100 is suitably secured as by aretaining nut 102. Arcuate movement of lever 100 is accomplished bysuitable means such as a brake operating cable, as is well known in theart, to obtain rotatable movement of shaft 94.

The inner end 104 of shaft 94 is recessed to the side of the threadedend of screw 90 in spaced relation thereto so that the end 104 isengageable with aside surface 106 of a clutch plate member 108. Member108 has a clutch surface 110 axially opposite side surface 106 andaligned for engagement with clutch surface 112 of an adjusting nut 114.This nut is threaded on the screw 90 so that it rotates it also hasaxial movement imparted thereto. Clutch plate 108 has a notched lip 116which mates with the splines 88 of piston skirt 84 so that the clutchplate is axially slidable relative to the piston but is not rotatablerelative to the piston.

The shaft 94 has a center section formed to provide a flange 118 whichhas its outer periphery provided with a plurality of slots 120 and itssurface 122 facing base wall 56 formed to receive balls 124 of aball-ramp actuating mechanism 126. Mechanism 126 includes ball ramps 128formed in base wall 56, the ramp angle determining the mechanicaladvantage of the mechanically actuated system. The balls 124 arecircumferentially spaced by a ball cage 130.

An adjusting nut restrainer 132 has an inner end 134 fitting about theadjusting nut so as to permit rotation of the nut relative to therestrainer but preventing any substantial relative axial movementtherebetween. A snap'ring 136 and washer 138 are provided for thesepurposes. The restrainer 132 has fingers 140 extending axially from therestrainer end 134 through slots 142 formed in clutch plate 108 andthrough slots 120 of flange 118. The outer ends 144 of fingers 140 haveradially inwardly extending lips 146 so that the lips engage the surface122 of flange 118 to prevent axial movement of the restrainer, and,therefore, axial movement of the adjusting nut 114, toward the pistonhead 68 relative to shaft 94 beyond the predetermined distance set bythe distance between lips 146 and restrainer inner end 134. Therestrainer finger ends 144 also are abutable against base wall 56 sothat axial movement of the restrainer and adjusting nut in a directiontoward shaft 94 and away from piston head 68 is also limited.

A resilient member 148, formed as a rubber-like grommet, is receivedabout the outer end of actuating shaft 94 intermediate the outer side ofthe base wall 56 and the lever 100, the member 148 being compressed byaxial movement of the shaft 94 toward piston 58 as occasioned by actionof the ball-ramp actuating mechanism 126 when lever 100 is rotated inthe brake actuating direction. When the lever 100 is released, theresilient expanding action of member 148 urges the shaft 94 in adirection away from piston 58 to return the shaft to the brake releaseposition. Member 148 also serves as an additional seal between shaft 94and the housing 48.

When the brake assembly is actuated by the introduction of brakepressure into chamber 54, piston 58 is moved towarddisc 12 to engagebrake pad assembly 66 with the disc friction surface 36. As the pressureincreases, disc 12 is forced to slide toward brake pad assembly 64 andinto frictional engagement with the brake lining 74 of that padassembly. The braking forces exerted on the pad assemblies by therotating disc are transmitted from the linings to the shoes and then tothe caliper frame 38.

The pressure in chamber 54 also urges shaft 94 away from piston 58, thisforce being transmitted through the balls 124 of the ball-ramp assembly128. Therefore, there is no axial force exerted directly between thepiston 58 and the shaft 94. As piston 58 moves leftwardly, it movesthreaded screw 90 axially with it. Since the restrainer 132 will notpermit leftward movement of nut 114 after the restrainer lips 146 engagethe surface 122 of flange 118, further movement of the piston and itsscrew 90 causes nut 114 to rotate, thereby increasing the distancebetween the piston head and the nut in accordance with the amount oflining wear required to be taken up. When the brake is normally properlyadjusted, the amount of actual axial movement of nut 1 14 is controlledby the slight clearances available between lip 146 and flange surface122 and between the restrainer inner end 134 and the nut and washer 138.This will normally be only a few thousandths of an inch, the preciseamount merely being sufficient to assure release of the brake linings inrelation to disc 12 so that the linings do not drag on the disc with anundesirable amount of force when the brakes are released.

Upon release of the brake actuating pressure in chamber 54, piston 58moves slightly inwardly into chamber54 as the brake pads no longer exertbraking forces on the disc. The amountof movement is controlledprimarily by the clearance between restrainer end 144 and base wall 56and secondarily by the clearance between clutch surfaces 110 and 112.Since the clutch plate 108 is splined to the piston shaft 84, itnormally tends to move with the piston during actuation. Upon release,it will return to its position which is normally in free engagement withthe end 104 of shaft 94.

If the piston should try to move further backward, it must slide clutchplate 108 on splines 88. If the space between the clutch surfaces 110and 112 is taken up, the piston can retract no further since engagementof the clutch surfaces will prevent the nut 114 from rotating. Normallythis space is not taken up during hydraulic actuation and release sincethe normal position of flange 118 in relation to base wall 56 and theaxial thickness of lip 146 to end 144 are such that the axial limit ofmovement of restrainer 132 and nut 144 is reached beforehand.

During mechanical application of the brake, as when parking, forexample, lever is rotated by suitable means such as the pull of a brakecable attached to the lever and to a brake pedal or hand lever operatedby the vehicle operator. Rotation of lever 100 causes balls 124 to rideup on ramps 128 and, therefore, move flange 118, and with the shaft 94,in a closing direction in relation to piston 58. This is a leftwardmovement as viewed in the drawing. The shaft inner end 104 engagessurface 106 of clutch plate 108 and moves the clutch plate axially withit to take up the distance between clutch surfaces 110 and 112 and tofrictionally engage those surfaces. This engagement prevents rotationalmovement of adjusting nut 114 on screw 90, so that axial force istransmitted through the clutch plate and clutch surfaces and nut 1 14 toscrew 90 and then to piston 58 to move the piston toward disc 12concurrently with further leftward movement of actuating shaft 94.

When the mechanical brake system is released, resilient member 148,having been previously compressed during actuation, expands axially andmoves shaft 94 in an opening direction in relation to piston 58, seen asrightward movement in the drawing. At the same time, the shaft rotatesas the balls 124 roll back down the ball ramps 128. Piston 58 then movesrightwardly to a brake release position, with the clutch plate 108,adjusting nut 114, and nut restrainer 132 taking the same positions andactions as described above upon pressure release.

An embodiment of the invention has been disclosed and described in whichthe brake mechanism is adjusted during pressure actuation with theavailability of a mechanical brake actuation independently of pressureactuation.

What is claimed is:

1. A brake actuator and adjuster comprising:

a wheel cylinder formed in a housing and having a brake actuating pistonreciprocably received therein and cooperating therewith to define abrake actuating pressure chamber;

a high-lead screw secured to said piston and extending into saidpressure chamber;

an adjuster nut and clutch face member threaded on said screw for axialand rotational movement;

a mechanical actuator including a shaft extending into said pressurechamber in axial alignment with said piston and said screw and havingmeans for operatively mechanically imparting axial force and movementthereto toward said piston;

means limiting axial movement of said nut and clutch face member in onedirection relative to said shaft and in the other direction relative tosaid housing;

a clutch member mounted on said piston for axial movement relativethereto and having a clutch face engageable with the clutch face of saidnut-and clutch face member to prevent rotation of said nut and clutchface member relative to said piston upon sufficient axial movement andforce of 'said shaft toward said piston and to transmit further axialmovement and force of said shaft to said piston;

and means returning said shaft in an axial direction away from saidpiston when said mechanical actuator is released;

said adjuster nut and clutch face member maintaining adjustment of saidpiston by requisite rotational and axial movement thereof on said screwwhen said piston is moved by pressure in said chamber beyond the limitof movement set by said limiting means for said nut and clutch facemember.

2. A brake mechanism comprising:

a housing having a brake actuating piston reciprocably received thereinand cooperating therewith to define a pressure chamber, said pistonhaving a brake pad assembly on the outer side and a recess defined by apiston skirt on the inner side, the wall of said skirt defining saidrecess having a plurality of splines extending axially parallel to theaxis of piston movement in said housing;

a threaded member secured to said piston and extending through saidrecess coaxially with the axis of piston movement in said housing;

an adjusting nut threaded on said threaded member and rotatable relativethereto in screw relation, one side of said nut forming a clutch facesurface and the other side of said nut having an axially effectiverestrainer thereon which permits relative rotation of said nut;

a clutch plate splined to said piston skirt splines for axial movementrelative thereto and having a clutch face surface in axial movableengageable relation to said adjusting nut clutch face surface, andhaving a plurality of slots formed therein in circumferentially spacedrelation radially outward of said clutch face surface;

an actuating shaft rotatably and reciprocably mounted in said housingwith one end extending into said chamber and engaging said clutch plate,the other end extending outward of said housing and having an actuatinglever secured thereto to impart rotational movement to the shaft, and acenter portion having a flange thereon, the flange having a plurality ofaxially extending slots in the outer periphery thereof and one sidesurface formed to receive a plurality of rotatable balls of a ball-rampactuator;

a ball-ramp actuator including a plurality of rotatable balls receivedon said flange one side surface and ball ramps formed on said housingand a ball cage member circumferentially positioning said balls;

and means resiliently urging said shaft axially outward of said chamberaway from said piston and yieldably opposing axial movement of saidshaft occasioned by rotation of said actuating lever and action of saidball-ramp actuator;

said restrainer having a plurality of actuating fingers extendingaxially away from said piston through said clutch plate slots and saidshaft flange slots and formed with inwardly extending lips on the outerends thereof engaging said flange one side surface to effectivelyprevent axial movement of said adjuster nut relatively away from saidflange beyond a predetermined distance, said finger outer ends being inabuttable relation with said housing to effectively prevent axialmovement of said adjuster nut in a direction away from said pistonbeyond a predetermined position relative to said housing.

l k ID

1. A brake actuator and adjuster comprising: a wheel cylinder formed ina housing and having a brake actuating piston reciprocably receivedtherein and cooperating therewith to define a brake actuating pressurechamber; a high-lead screw secured to said piston and extending intosaid pressure chamber; an adjuster nut and clutch face member threadedon said screw for axial and rotational movement; a mechanical actuatorincluding a shaft extending into said pressure chamber in axialalignment with said piston and said screw and having means foroperatively mechanically imparting axial force and movement theretotoward said piston; means limiting axial movement of said nut and clutchface member in one direction relative to said shaft and in the otherdirection relative to said housing; a clutch member mounted on saidpiston for axial movement relative thereto and having a clutch faceengageable with the clutch face of said nut and clutch face member toprevent rotation of said nut and clutch face member relative to saidpiston upon sufficient axial movement and force of said shaft towardsaid piston and to transmit further axial movement and force of saidshaft to said piston; and means returning said shaft in an axialdirection away from said piston when said mechanical actuator isreleased; said adjuster nut and clutch face member maintainingadjustment of said piston by requisite rotational and axial movementthereof on said screw when said piston is moved by pressure in saidchamber beyond the limit of movement set by said limiting means for saidnut and clutch face member.
 2. A brake mechanism comprising: a housinghaving a brake actuating piston reciprocably received therein andcooperating therewith to define a pressure chamber, said piston having abrake pad assembly on the outer side and a recess defined by a pistonskirt on the inner side, the wall of said skirt defining said recesshaving a plurality of splines extending axially parallel to the axis ofpiston movement in said housing; a threaded member secured to saidpiston and extending through said recess coaxially with the axis ofpiston movement in said housing; an adjusting nut threaded on saidthreaded member and rotatable relative thereto in screw relation, oneside of said nut forming a clutch face surface and the other side ofsaid nut having an axially effective restrainer thereon which permitsrelative rotation of said nut; a clutch plate splined to said pistonskirt splines for axial Movement relative thereto and having a clutchface surface in axially movable engageable relation to said adjustingnut clutch face surface, and having a plurality of slots formed thereinin circumferentially spaced relation radially outward of said clutchface surface; an actuating shaft rotatably and reciprocably mounted insaid housing with one end extending into said chamber and engaging saidclutch plate, the other end extending outward of said housing and havingan actuating lever secured thereto to impart rotational movement to theshaft, and a center portion having a flange thereon, the flange having aplurality of axially extending slots in the outer periphery thereof andone side surface formed to receive a plurality of rotatable balls of aball-ramp actuator; a ball-ramp actuator including a plurality ofrotatable balls received on said flange one side surface and ball rampsformed on said housing and a ball cage member circumferentiallypositioning said balls; and means resiliently urging said shaft axiallyoutward of said chamber away from said piston and yieldably opposingaxial movement of said shaft occasioned by rotation of said actuatinglever and action of said ball-ramp actuator; said restrainer having aplurality of actuating fingers extending axially away from said pistonthrough said clutch plate slots and said shaft flange slots and formedwith inwardly extending lips on the outer ends thereof engaging saidflange one side surface to effectively prevent axial movement of saidadjuster nut relatively away from said flange beyond a predetermineddistance, said finger outer ends being in abuttable relation with saidhousing to effectively prevent axial movement of said adjuster nut in adirection away from said piston beyond a predetermined position relativeto said housing.